FPESA Research Paper Assessment: “Carbon Legacies” and the Link Between Childbearing and Climate Change

Project Director’s note: On August 18, National Public Radio ran a segment on the efforts of bioethical philosopher Travis Rieder to justify the concept of “population engineering” to head off catastrophic climate change. Rieder and two co-authors of a forthcoming peer-reviewed paper define the concept as “the intentional manipulation of the size and structure of human populations.” While this unpublished paper has not been assessed by the FPESA project, the assessment posted here treats an earlier paper relevant to the provocative policy proposal Rieder and his colleagues are advancing.

Under medium scenarios of future fertility and carbon emissions, having a child generally leads to the addition of many times the amount of emissions that an individual personally contributes during her or his lifetime, these authors calculate. As a supplement to advice on how lifestyle decisions can reduce an individual’s lifetime emissions, this paper proposes adding responsibility for the impacts of what could be called a reproductive “afterlife”: those emissions caused by each biological child and that child’s descendants until the original parent’s genetic line dies out. The authors estimate ranges for what they call “legacy” emissions—those that an average individual can expect to be effectively responsible for in having a child—in the 11 most populous countries in the world.

For the United States, having a child multiplies such emissions by 5.7 times the individual’s own lifetime emissions.

For the United States, having a child multiplies such emissions by 5.7 times the individual’s own lifetime emissions, assuming middle-range fertility and emissions projections. In Japan, which has lower per capita emissions and a lower fertility rate than the United States does today, the average projected legacy emissions would be 2.4 times per child. The calculations are based on a pro-rata calculation of surviving descendants’ emissions based on their genetic connection to the original parent—i.e., half a child’s emissions are assigned to the parent, one-quarter a grandchild’s, and so on, until there are no further descendants. (See Figure.) Average lineages in the model last about four centuries before a parent’s last descendant dies without reproducing, based on the fertility and life-expectancy projections for each of the 11 countries.

Illustration from the paper (page 15). Used by permission.

The authors use these calculations to show that having a child causes long-term emissions additions that much more than offset any emissions savings from plausible behavior changes during one’s lifetime. They conclude that such behavior changes are no less needed, because their impact is more immediate than those of legacy emissions. They nonetheless call for more attention to the climate change impacts of long-term emissions legacies that result from reproduction.

Key quotes: “Our basic premise is that a person is responsible for the carbon emissions of his descendants, weighted by their relatedness to him. . . . Under the constant-emissions scenario, the average emissions added by having a single child range from 56 tons (Bangladesh) to 9,441 tons (United States). . . . Clearly, the potential savings from reduced reproduction are huge compared to the savings that can be achieved by changes in lifestyle. . . . This is not to say that lifestyle changes are unimportant; in fact, they are essential, since immediate reductions in emissions worldwide are needed to limit the damaging effects of climate change that are already being documented. The amplifying effect of an individual’s reproduction documented here implies that such lifestyle changes must propagate through future generations in order to be fully effective, and that enormous future benefits can be gained by immediate changes in reproductive behavior.”

“Clearly, the potential savings from reduced reproduction are huge compared to the savings that can be achieved by changes in lifestyle.”

Assessment: The idea that having a child will affect future environmental impacts is hardly new to discussions of humans’ impacts on the environment. This is the basis of most attempts to calculate the impact of population growth on climate change, water scarcity, and other kinds of environment change or natural resource availability. What makes this paper unusual is the authors’ emphasis on an individual parent having a single new child, with calculations of what they call the “legacy” of such an instance of childbearing. So far as the FPESA project has been able to determine, this is the first use of the concept of a legacy effect, which was later used by Usman Khan and Jim A. Nicell, 2014 (see the FPESA assessment posted on February 12 ), to study the impact of contraception on estrogen pollution.

Although the overall methodology and message of this paper may be controversial—some may disagree with the premise that parents are responsible for their descendants’ environmental behavior and impacts—this is an important, possibly even a landmark, paper. Individual reproductive decisions and behavior are central to the thesis that feasible differences in future population size will have significant long-term effects on the environment, a key FPESA sub-hypothesis.

Can assumptions about fertility and per capita emissions be meaningful four centuries into the future?

The idea that parents leave an environmental legacy through reproduction is simultaneously logical yet questionable when applied quantitatively. Can assumptions about fertility and per capita emissions be meaningful four centuries into the future? Perhaps not—yet, through such imaginative efforts, researchers can provide some measure of how individual reproduction and fertility may matter to the environment that future generations experience. The quantification of environmental legacy is unlikely to be valid in considering how family planning may affect environmental sustainability, but the concept itself is valid. This paper pioneers in its exploration.

The following annotation and assessment is excerpted from the just-released report of the Family Planning and Environmental Sustainability Assessment (FPESA) project. The report contains selected annotations from 939 peer-reviewed articles reviewed for potential relevance to the hypothesis that family planning supports environmental sustainability. The annotations are written by project director Robert Engelman with input from members of the project team and, where indicated, members of the project’s international network of research assessors.

Travis and Sadiye Rieder read a book with their 2-year-old daughter, Sinem, in their Maryland home. Travis is a philosopher and ethicist who argues against having too many children, for moral and environmental reasons. His wife always wanted to have a big family. (Ariel Zambelich/NPR)